1. Field of the Invention
The present invention relates generally to the treatment of process streams and, more particularly, to catalytic wet oxidation and hydrolysis systems and methods for the treatment of undesirable constituents therein.
2. Description of Related Art
To meet energy and manufacturing needs, oil and gas are routinely extracted from underground sources. Conventional oil and gas extraction is a water intensive process. Produced water is typically unfit for discharge into local water sources and may be injected into underground wells for disposal. Alternatively, produced water may be treated to render it suitable for a variety of uses.
In a conventional oil or gas extraction operation, injected water may be used to drive oil or gas to the surface at a well head. The injected water and/or the existing water in the formation surfaces as a mixture, or emulsion, known as “produced water” that includes the oil and gas products. The water portion and oil portion of the produced water are separated by various unit operations. Portions of the separated water stream may undergo different treatment operations depending on their intended use. Intended uses of the water stream may include reinjection to permanent well disposal or waterflooding. Alternatively, the intended use may require an improved water quality, such as for irrigation.
Characteristics and components of the produced water may be detrimental to the piping system carrying it. For example, in the context of deep well applications, in colder temperatures organics from the produced water form organic ice (hydrates) on the walls of pipes carrying produced water, particularly where there are large pressure drops.
The problem of organic ice has in the past been addressed through the addition of glycols to the produced water, however that process is expensive and requires relatively high concentrations of glycols to be effective. Furthermore, the glycols must subsequently be removed, adding an additional step to the overall treatment process.
Kinetic hydrate inhibitors “KHIs” (also known as “LDHI”, low dose hydrate inhibitors) serve as an alternative to glycols for inhibiting icing, where they can be introduced in lower concentrations.
While KHIs enjoy certain advantages over glycols they also have disadvantages. For example, KHIs have a cloud point generally in the range of 40-80° C.
A produced water solution in that temperature range may become cloudy from precipitation of KHI. Some regulatory bodies fear that such a cloudy solution could plug off reservoirs and have therefore banned deep well reinjection of produced waters containing KHI. As a result their use in such applications has been limited.
KHI is a class of high weight organic polymers. KHI share some similar properties to another class of high weight polymers present in certain produced waters—HPAM (hydrolyzed polyacrylamide). HPAM increases viscosity to help remove oil from underground often as part of a more general process referred to as enhanced oil recovery (EOR). The increased viscosity created by the HPAM to aid in oil or gas removal subsequently becomes an impediment to separation processes applied to the produced water, at it forms emulsions that are difficult to separate. As a result, HPAM is preferably removed at some stage during produced water treatment to reduce the viscosity of the stream and aid in separation.
KHI and HPAM each contribute to the chemical oxygen demand (COD) of produced water. Other sources of COD in produced water include light hydrocarbons and other organics.